1. Technical Field
The preset invention relates to an industrial robot and, more specifically, to an industrial robot provided with an imaging device of a visual sensor for detecting a working tool and a working position.
2. Description of the Related Art
In an industrial robot (hereinafter referred to simply as a robot), there are many cases wherein an imaging device of a visual sensor is mounted for detecting a working tool and a working position (for example, a digital CCD camera). For example, when a robot program is made on off-line, there is usually an error between an actual operation path for this program and a desired operation path, and for the purpose of correcting the same, a method for mounting an imaging device of a visual sensor for detecting the working position in the vicinity of the working tool and correcting a teaching point by using detected data obtained through the imaging device (for example, see Japanese Unexamined Patent Publication No. 10-128538).
When the visual sensor is actually supported in the vicinity of the operative tool, however, it is liable to interfere with a workpiece or others because it has a considerable size in the vertical and horizontal directions. Accordingly, it is difficult to obtain the same operation path during the actual operation (for example, welding), whereby there has been a limitation in an applicable program. Also, a conventional sensor supporting structure (a structure for supporting an imaging device) may interfere with a part of a body of the robot on a side of a torch cable for supporting a welding cable or assist gas to an arc-welding torch.
In a more concrete prior art, an imaging device and a working tool holding member are attached by well-known attachment means (not shown) using adhesive, screws or others to a distal end of a wrist flange supported by a robot arm. The working tool supported by the working tool holding member is, for example, an arc welding torch (hereinafter merely referred to as a torch) used for corner welding or other work. When the corner welding is carried out in a narrow and complicated portion of a workpiece, part of the imaging device (particularly, a distal end portion) may approach the workpiece and interfere therewith. Further, interference between the torch and the body of the robot may occur.
To avoid such interference, in the above-mentioned prior art, a different structure of the working tool is used in the production from that used in the teaching, or the imaging device is removed if necessary. Such a countermeasure, however, is problematic in that the teaching cannot be corrected as in the production. Alternatively, the working tool may be of a detachable type to allow the working tool to be detached from the distal end of the wrist and, instead, the imaging device of the visual sensor is mounted thereto so that the interference with the peripheral equipment is temporarily eliminated. In the latter case, there is another problem caused by the attachment error of the working tool or in that it is impossible during the teaching to correct the deviation of the welded position due to the change of wire bending due to a posture of the robot (see FIG. 4 and the explanation thereof described later).
In this regard, relating to the embodiments of the present invention described later, IEEE TRANSACTIONS ON ROBOTICS AND AUTOMATION (Vol. 5, No. 3, June 1989) “A New Technique for Fully Autonomous and Efficient 3D Robotics Hand/Eye calibration” is cited as a prior art.